Slush molding composition

ABSTRACT

A thermoplastic polypropylene composition comprising polypropylene, a hydrogenated block copolymer, 3 to 6 wt % high density polyethylene, 5 to 10 wt % of a processing oil, and greater than or equal to 3 wt % of a surface modifier comprising an ultra high molecular weight polydialkyl siloxane, an ultra-high molecular weight polydialkyl siloxane in combination with silica, a polyolefin siloxane or a combination thereof, wherein weight percent is based on the total weight of the composition.

BACKGROUND

Thermoplastic polyolefin compositions are actively pursued asalternative materials for fabricated articles made of polyvinylchloride, thermoplastic polyurethane, and/or recycled polymers. In theautomotive field, thermoplastic polyolefin compositions have been usedfor the fabrication of articles such as interior sheathing, includinginstrument panel skins, door panels, air bag covers and seat covers.Many of these articles have surface appearances and designs with complexsurface characteristics, such as contours and geometric technicalgrains.

Rotational molding processes involving a rotating mold have been foundto be useful in the production of a variety of molded articles. Slushmolding is a type of rotational molding wherein less than the entireinterior surface of the rotating mold is heated. That is, in a slushmolding process, a preheated mold is in continuous contact with areservoir holding unheated polymer powder. As the polymer powdercontacts the heated mold surface, it melts and fills all aspects of themold. The relevant portion of the mold surface must therefore be heatedto a temperature sufficient to obtain a desirable melt viscosity in thepolymer to be molded.

Slush molding processes have been found to be particularly advantageousfor the production of molded articles with complex surfacecharacteristics. Ideally, a slush molding composition needs to have goodmelt flow (low melt viscosity at molding temperatures) as well as littleor no degradation at slush molding temperatures. It is important thatthe surface of the molded article be capable of withstanding the wearand tear associated with use of the article. Specifically, it isessential that the molded article have robust scratch and marproperties.

There is thus a need in the art for a thermoplastic polyolefincomposition having good melt flow, little or no degradation duringmolding and good scratch and mar properties

BRIEF DESCRIPTION

The above described and other features are exemplified by the followingfigures and detailed description.

In one embodiment, the disclosed composition comprises polypropylene, ahydrogenated block copolymer, 3 to 6 weight percent (wt %) high densitypolyethylene, 5 to 10 wt % of a processing oil, and at least 3 wt % of asurface modifier comprising an ultra-high molecular weight polydialkylsiloxane, an ultra-high molecular weight polydialkyl siloxane incombination with silica, a polyolefin siloxane or a combination thereof,wherein weight percent is based on the total weight of the composition.

BRIEF DESCRIPTION OF THE DRAWINGS

Refer now to the figures, which are exemplary embodiments, and whereinthe like elements are numbered alike.

FIGS. 1-4 contains pictures which demonstrate the results of testperformed on the Examples as discussed below.

DETAILED DESCRIPTION

Slush molding compositions with good resistance to scratch and mar havebeen long sought. When surface modifying additives were first developedto address scratch and mar issues it was recognized that the scratch andmar resistance should be robust and long lived. As shown herein, scratchand mar resistance is not an automatic result of employing surfacemodifying additives. The effect of the surface modifying additive isspecific to the thermoplastic composition and surface modifyingadditives that were expected to work in the thermoplastic polyolefincomposition were in fact unsuccessful as further explained and describedbelow. It was further discovered that surface modifiers alone wereinsufficient and high density polyethylene was required for scratch andmar resistance.

The polypropylene can be homopolypropylene or a polypropylene copolymer.Copolymers of polypropylene and rubber or block copolymers are sometimesreferred to as impact modified polypropylene. Such copolymers aretypically heterophasic and have sufficiently long sections of eachcomponent to have both amorphous and crystalline phases. Additionallythe polypropylene may comprise a combination of homopolymer andcopolymer, a combination of homopolymers having different meltingtemperatures, or a combination of homopolymers having different meltflow rates.

In one embodiment the polypropylene comprises a crystallinepolypropylene such as isotactic polypropylene. Crystallinepolypropylenes are defined as polypropylenes having a crystallinitycontent greater than or equal to 20%, or, more specifically, greaterthan or equal to 25%, or, even more specifically, greater than or equalto 30%. Crystallinity may be determined by differential scanningcalorimetry (DSC).

In some embodiments the polypropylene has a melting temperature greaterthan or equal to 134° C., or, more specifically, greater than or equalto 140° C., or, even more specifically, greater than or equal to 145° C.

The polypropylene has a melt flow rate (MFR) of 60 to 1200 grams per 10minutes (g/10 min). Within this range the melt flow rate may be greaterthan or equal to 70 g/10 min. Also within this range the melt flow ratemay be less than or equal to 600, or, more specifically, less than orequal to 400, or, more specifically, less than or equal to 200 g/10 min.Melt flow rate can be determined according to ASTM D1238 using eitherpowdered or pelletized polypropylene, a load of 2.16 kilograms and atemperature of 230° C.

The thermoplastic polyolefin composition comprises 20 to 30 wt. %polypropylene based on the total weight of the composition. Within thisrange the amount of polypropylene can be greater than or equal to 22 wt%. Also within this range the amount of polypropylene can be less thanor equal to 27 wt %, or, less than or equal to 25 wt %.

The hydrogenated block copolymer is a copolymer comprising (A) at leastone block derived from an alkenyl aromatic compound and (B) at least oneblock derived from a conjugated diene, in which the aliphaticunsaturated group content in the block (B) is reduced by hydrogenation.The arrangement of blocks (A) and (B) includes a linear structure and aso-called radial teleblock structure having branched chains.

Preferred of these structures are linear structures embracing diblock(A-B block), triblock (A-B-A block or B-A-B block), tetrablock (A-B-A-Bblock), and pentablock (A-B-A-B-A block or B-A-B-A-B block) structuresas well as linear structures containing 6 or more blocks in total of Aand B. More preferred are diblock, triblock, and tetrablock structures,with the A-B diblock and A-B-A triblock structures being particularlypreferred.

The alkenyl aromatic compound providing the block (A) is represented byformula:

wherein R2 and R3 each independently represent a hydrogen atom, a C1-C8alkyl group, a C2-C8 alkenyl group, or the like; R4 and R8 eachindependently represent a hydrogen atom, a C1-C8 alkyl group, a chlorineatom, a bromine atom, or the like; and R5-R7 each independentlyrepresent a hydrogen atom, a C1-C8 alkyl group, a C2-C8 alkenyl group,or the like, or R4 and R5 are taken together with the central aromaticring to form a naphthyl group, or R5 and R6 are taken together with thecentral aromatic ring to form a naphthyl group.

Specific examples, of the alkenyl aromatic compounds include styrene,p-methylstyrene, alpha-methylstyrene, vinylxylenes, vinyltoluenes,vinylnaphthalenes, divinylbenzenes, bromostyrenes, chlorostyrenes, andthe like, and combinations comprising at least one of the foregoingalkenyl aromatic compounds. Of these, styrene, alpha-methylstyrene,p-methylstyrene, vinyltoluenes, and vinylxylenes are preferred, withstyrene being more preferred.

Specific examples of the conjugated diene include 1,3-butadiene,2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, andthe like. Preferred among them are 1,3-butadiene and2-methyl-1,3-butadiene, with 1,3-butadiene being more preferred.

In addition to the conjugated diene, the hydrogenated block copolymermay contain a small proportion of a lower olefinic hydrocarbon such as,for example, ethylene, propylene, 1-butene, dicyclopentadiene, anon-conjugated diene, or the like.

The alkenyl aromatic content may be 1 to about 30 weight based on thetotal weight of the hydrogenated block copolymer. Within this range, thealkenyl aromatic content can be greater than or equal to 5 weightpercent, or, greater than or equal to 10 weight percent. Also withinthis range, the alkenyl aromatic content can be less than or equal to 20weight percent, or, less than or equal to 15 weight percent.

There is no particular limitation on the mode of incorporation of theconjugated diene in the hydrogenated block copolymer backbone. Forexample, when the conjugated diene is 1,3-butadiene, it may beincorporated with about 1% to about 99% 1,2-incorporation with theremainder being 1,4-incorporation.

The hydrogenated block copolymer is preferably hydrogenated to such adegree that fewer than 50%, more preferably fewer than 20%, yet morepreferably fewer than 10%, of the unsaturated bonds in the aliphaticchain moiety derived from the conjugated diene remain unreduced. Thearomatic unsaturated bonds derived from the alkenyl aromatic compoundmay be hydrogenated to a degree of up to about 25%.

The hydrogenated block copolymer preferably has a number averagemolecular weight of about 5,000 to about 500,000 AMU, as determined bygel permeation chromatography (GPC) using polystyrene standards. Withinthis range, the number average molecular weight may preferably be atleast about 10,000 AMU, more preferably at least about 30,000 AMU, yetmore preferably at least about 45,000 AMU. Also within this range, thenumber average molecular weight may preferably be up to about 300,000AMU, more preferably up to about 200,000 AMU, yet more preferably up toabout 150,000 AMU.

The molecular weight distribution of the hydrogenated block copolymer asmeasured by GPC is not particularly limited. The copolymer may have anyratio of weight average molecular weight to number average molecularweight.

Some of these hydrogenated block copolymers have a hydrogenatedconjugated diene polymer chain to which crystallinity is ascribed.Crystallinity of the hydrogenated block copolymer can be determined bythe use of a differential scanning calorimeter (DSC), for example,DSC-II Model manufactured by Perkin-Elmer Co. Heat of fusion can bemeasured by a heating rate of, for example, 10° C./min in an inert gasatmosphere such as nitrogen. For example, a sample may be heated to atemperature above an estimated melting point, cooled by decreasing thetemperature at a rate of 10° C./min, allowed to stand for about 1minute, and then heated again at a rate of 10° C./min.

The hydrogenated block copolymer may have any degree of crystallinity.In view of a balance of mechanical strength of the resulting resincomposition, those hydrogenated block copolymers having a melting pointof about −40° C. to about 200° C. or having no definite melting point(i.e., having non-crystallinity), as measured according to theabove-described technique, are preferred. More preferably, thehydrogenated block copolymers have a melting point of at least about 0°C., yet more preferably at least about 20° C., still more preferably atleast about 50° C.

The hydrogenated block copolymer may have any glass transitiontemperature (Tg) ascribed to the hydrogenated conjugated diene polymerchain. From the standpoint of low-temperature impact strength of theresulting resin composition, it preferably has a Tg of up to about 0°C., more preferably up to about −120° C. The glass transitiontemperature of the copolymer can be measured by the aforesaid DSC methodor from the visco-elastic behavior toward temperature change as observedwith a mechanical spectrometer.

Particularly preferred hydrogenated block copolymers are thestyrene-(ethylene-butylene) diblock, styrene-(ethylene-propylene)diblock, styrene-(ethylene-propylene)-styrene triblock, andstyrene-(ethylene-butylene)-styrene triblock copolymers.

Suitable hydrogenated block copolymers include those commerciallyavailable as, for example, KRATON® from Kraton Polymers (formerly adivision of Shell Chemical Company), and TUFTEC® from Asahi Chemical. Itis explicitly contemplated that a mixture of hydrogenated blockcopolymers having a weight average alkenyl aromatic content of 1 to 30weight percent based on the total weight of hydrogenated blockcopolymers. For example a mixture of a 30 grams of a first hydrogenatedblock copolymer having an alkenyl aromatic content of 50 parts by weightand 70 grams of a second hydrogenated block copolymer having an alkenylaromatic content of 20 parts by weight would have a weight averagealkenyl aromatic content of 29 as calculated by (0.3×50)±(0.7×20).

The hydrogenated block copolymer can be present in an amount of 50 to 60weight percent, based on the total weight of the composition. Withinthis range the block copolymer can be present in an amount greater thanor equal to 52 weight percent. Also within this range the hydrogenatedblock copolymer can be present in an amount less than or equal to 57weight percent.

The high density polyethylene (HDPE) can be homo polyethylene or apolyethylene copolymer. Additionally the high density polyethylene maycomprise a combination of homopolymer and copolymer, a combination ofhomopolymers having different melting temperatures, or a combination ofhomopolymers having a different melt flow rate and generally having adensity of 0.941 to 0.965 g/cm3.

In some embodiments the high density polyethylene has a meltingtemperature greater than or equal to 124° C., or, more specifically,greater than or equal to 126° C., or, even more specifically, greaterthan or equal to 128° C.

The high density polyethylene has a melt flow rate (MFR) greater than orequal to 20 grams per 10 minutes and less than or equal to 40 grams perten minutes (g/10 min). Within this range the melt flow rate may begreater than or equal to 25 g/10 min. Also within this range the meltflow rate may be less than or equal to 35 g/10 min. Melt flow rate canbe determined according to ASTM D1238 using either powdered orpelletized polyethylene, a load of 2.16 kilograms and a temperature of190° C.

The composition may comprise high density polyethylene in an amount of 3to 6 wt %, based on the total weight of the composition. Within thisrange the amount of high density polyethylene may be greater than orequal to 3.5 wt %. Also within this range the amount of polyolefin maybe less than or equal to 5.5 wt %.

Illustrative examples of suitable processing oils are those compatibleprocessing oils that include hydrocarbon based oils comprising mainlyparaffinic components. In one embodiment, the processing oil will be anonaromatic processing oil.

Suitable process oils have an average molecular weight (calculated fromthe kinematic viscosity per ASTM D2502) in the range of about 100 toabout 1000. The average molecular weight of the process oil should beselected to avoid migration from the composition in normal service useconditions. In one embodiment, the average molecular weight of theprocessing oil will be from 400 to 800.

Commercially available examples of suitable processing oils includeParalux processing oil and Hydrobrite processing oil, respectivelycommercially available from Chevron and Crompton.

Illustrative examples of processing oils include hydrocarbon based oilscomprising mainly paraffinic components. The processing oil can be anonaromatic processing oil.

Suitable process oils have an average molecular weight (calculated fromthe kinematic viscosity per ASTM D2502) of 100 to 1000. The averagemolecular weight of the process oil should be selected to avoidmigration from the composition in normal service use conditions. Theaverage molecular weight of the processing oil can be from 400 to 800.

Commercially available examples of suitable processing oils includeParalux processing oil and Hydrobrite processing oil, respectivelycommercially available from Chevron and Crompton.

The processing oil is present in an amount of 5 to 10 weight percent,based on the total weight of the composition. Within this range theprocessing oil can be present in an amount greater than or equal to 6 wt%. Also within this range the processing oil can be present in an amountless than or equal to 9 wt %.

As mentioned above surface modifiers include ultra-high molecular weightpolydialkyl siloxanes such as polydimethyl siloxanes, ultra highmolecular weight polydialkyl siloxanes in combination with silica,polyolefin siloxanes and combinations thereof. An ultra-high molecularweight polydialkyl siloxane has a molecular weight greater than or equalto 40,000, more specifically, greater than or equal to 100,000, morespecifically greater than or equal to 200,000. The polydialkyl siloxanemolecular weight can be less than or equal to 600,000. The ultra-highmolecular weight polydialkyl siloxane can be included as part of amasterbatch, particularly a polyolefin masterbatch such as apolypropylene masterbatch.

The above described surface modifiers are commercially available asMB-50 from Dow Silicone, Genioplast S Pellets from Wacker Chemie, andTegomer Antiscratch L from Evonik.

The surface modifier can be used in an amount greater than or equal to 3weight percent, based on the total weight of the composition. Thesurface modifier can be present in an amount less than or equal to 10weight percent, based on the total weight of the composition.

The composition may further comprise colorants, antioxidants, lightstabilizers and the like. Typically the colorant is present in an amountless than of equal to 5 weight percent, based on the total weight of thecomposition. The other additives may be present in amounts less than orequal to 1 weight percent, based on the total weight of the composition.

In general, the invention may alternately comprise, consist of, orconsist essentially of, any appropriate components herein disclosed. Theinvention may additionally, or alternatively, be formulated so as to bedevoid, or substantially free, of any components, materials,ingredients, adjuvants or species used in the prior art compositions orthat are otherwise not necessary to the achievement of the functionand/or objectives of the present invention.

The invention is further illustrated by the following non-limitingexamples

EXAMPLES Examples 1-7

Examples 1-7 were made using a base composition recipe as shown in Table1.

TABLE 1 Amount (in weight Material/Supplier Description percent)Polypropylene AP5995- Polypropylene having an 26.3 HA available fromFlint MFR of 100 g/10 min. Hills Resources Kraton G 1643 available Ahydrogenated block 43.9 from Kraton Polymers copolymer having an alkenylaromatic content of 20%. Kraton G 1726 A hydrogenated block 17.5copolymer having an alkenyl aromatic content of 30%. Color concentratefrom 3.5 Americhem Ebony B-2215 from Ciba Heat stabilizer 0.2Tinuvin-234 from Ciba UV stabilizer 0.2 Uvinal 5050H from BASF Lightstabilizer 0.2 Cyasorb 3853S from Light stabilizer 0.3 CYTEC Zincstearate 0.4 Paralux 6001R Process Oil 7.5

The base composition was combined with 5 weight percent of varioussurface modifiers (shown in Table 2), in some cases with 5 weightpercent HDPE (also shown in Table 2) and in some cases without HDPE.

TABLE 2 Genioplast Pellet S from Wacker Ultra high molecular weightChemie polydimethylsiloxane and silica MB50-001 from Dow Silicones Ultrahigh molecular weight polydimethylsiloxance masterbatch in polypropyleneIrgasurf SR 100B from BASF Functionalized polysiloxane Tegomer H SI 6440from Evonik Copolyester siloxane Tegomer Antiscratch L from Polyolefinsiloxane Evonik OnCap from PolyOne Erucamide ALATHON H6030 from EquistarHDPE having a melt index of 30 g/10 min at 190° C.

The formulations are shown in Table 3. The materials were compressionmolded and then evaluated for scratch and mar resistance by FordLaboratory Test Method BN 108-04. Presence or absence of scuff marks wasdetermined visually. A clear circular pattern was rated as a “scuff”(S), a faint circular pattern was rated as “slight scuff” (SS) and nocircular pattern was rated as “no scuff” (NS). Pictures of the scufftests are shown in FIGS. 1 and 2.

TABLE 3 Base* 1 2* 3* 4* 5 6 7* Genioplast S — — — X — — X — MB50 — X —— — — — — Irgasurf — — X — — — — — Tegomer 6440 — — — — X — — — TegomerAntiscratch L — — — — — X — — OnCap — — — — — — — X HDPE — X X — X X X —Rating S NS S SS S NS NS S *Comparative Example

As can be seen from the above results, not all surface modifiers aresuccessful in preventing scratch and mar in the thermoplasticpolypropylene composition. Only ultra-high molecular weight polydialkylsiloxane or polyolefin siloxane in combination with HDPE is successfulin providing scratch resistance.

Example 8

The overall formulation using Genioplast S and HDPE was reformulated.The composition is shown in Table 4. Amounts are in weight percent basedon the total weight of the composition

TABLE 4 Polypropylene 23.5 Kraton G 1643 39.1 Kraton G 1726 15.7 Colorconcentrate 3.1 B-2215 from Ciba 0.2 Tinuvin-234 from Ciba 0.2 Uvinal5050H from BASF 0.2 Cyasorb 3853S from CYTEC 0.3 Zinc stearate 0.4Paralux 6001R 8.4 HDPE 4.5 Genioplast S 4.5

The composition was slush molded and subjected to the scuff testdescribed above. After 250 cycles at 900 grams no marks were seen. Thecomposition was also compression molded and tested by the 5 fingerscratch test according to standard Ford protocol. This test showed nomarks at 2 and 3 Newtons. Results are also shown in FIG. 3. A slush castskin was subjected to the fingernail scratch test according to BMWmethod GS 97034-2 and no marking was seen until 15 Newton force wasapplied. Results are shown in FIG. 4.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other (e.g., ranges of“up to 25 wt. %, or, more specifically, 5 wt. % to 20 wt. %”, isinclusive of the endpoints and all intermediate values of the ranges of“5 wt. % to 25 wt. %,” etc.). “Combination” is inclusive of blends,mixtures, alloys, reaction products, and the like. Furthermore, theterms “first,” “second,” and the like, herein do not denote any order,quantity, or importance, but rather are used to denote one element fromanother. The terms “a” and “an” and “the” herein do not denote alimitation of quantity, and are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. The suffix “(s)” as used herein is intended toinclude both the singular and the plural of the term that it modifies,thereby including one or more of that term (e.g., the film(s) includesone or more films). Reference throughout the specification to “oneembodiment”, “another embodiment”, “an embodiment”, and so forth, meansthat a particular element (e.g., feature, structure, and/orcharacteristic) described in connection with the embodiment is includedin at least one embodiment described herein, and may or may not bepresent in other embodiments. In addition, it is to be understood thatthe described elements may be combined in any suitable manner in thevarious embodiments.

While particular embodiments have been described, alternatives,modifications, variations, improvements, and substantial equivalentsthat are or may be presently unforeseen may arise to applicants orothers skilled in the art. Accordingly, the appended claims as filed andas they may be amended are intended to embrace all such alternatives,modifications variations, improvements, and substantial equivalents.

I/we claim:
 1. A thermoplastic polypropylene composition comprisingpolypropylene, a hydrogenated block copolymer, 3 to 6 wt % high densitypolyethylene, 5 to 10 wt % of a processing oil, and greater than orequal to 3 wt % of a surface modifier comprising an ultra-high molecularweight polydialkyl siloxane, an ultra-high molecular weight polydialkylsiloxane in combination with silica, a polyolefin siloxane or acombination thereof, wherein weight percent is based on the total weightof the composition.
 2. The composition of claim 1, wherein thepolypropylene is a copolymer.
 3. The composition of claim 1, wherein thepolypropylene has a melt flow rate of 60 to 1200 grams per 10 minutes asdetermined according to ASTM D1238 using either powdered or pelletizedpolypropylene, a load of 2.16 kilograms and a temperature of 230° C. 4.The composition of claim 1, wherein the polypropylene is present in anamount of 20 to 30 wt %, based on the total weight of the composition.5. The composition of claim 1, wherein the hydrogenated block copolymerhas an alkenyl aromatic content of 1 to about 30 weight percent based onthe total weight of the hydrogenated block copolymer.
 6. The compositionof claim 1, wherein the hydrogenated block copolymer is present in anamount of 50 to 60 weight percent, based on the total weight of thecomposition.
 7. The composition of claim 1, wherein the surface modifiercomprises an ultra-high molecular weight polydialkyl siloxane incombination with silica.